1. Field of the Invention
The present invention relates to a frequency converter in transceivers used in communication systems.
2. Description of the Related Art
In any communication system, a complete transceiver unit having a transmission function and a reception function must have a frequency converter with an up-conversion capability to convert IF (intermediate frequency) signals to RF (radio frequency) signals and a down-conversion capability to convert RF signals to IF signals. The present invention relates to such a frequency converter having an up-conversion capability and a down-conversion capability.
FIG. 5 shows a conventional frequency converter of this type comprised by a separately provided upconverter 29 and a down converter 30 and a common local oscillator (generator) 38 shared by the upconverter 29 and the downconverter 30.
Upconverter 29 has an IF input port 31, which is connected to the input terminal of an input matching circuit 32. The output terminal of the input matching circuit 32 is connected to a mixer circuit 32, which is also connected to a local oscillator 38 and outputs RF signals by receiving IF signals from the matching circuit 32 and mixing with local oscillator signals 37 (having a frequency F0) from the local oscillator 38. The output terminal of the mixer circuit 33 is connected to the input terminal of the output matching circuit 35. Output terminal of the output matching circuit 35 is connected to the RF output port 36.
Downconverter 30 has an RF input port 39, which is connected to the input terminal of an input matching circuit 40. The output terminal of the input matching circuit 40 is connected to a mixer circuit 41, which is also connected to the local oscillator 38 and outputs IF signals by receiving IF signals from the matching circuit 40 and mixing with local oscillator signals 45 (having the same frequency F0 as the local oscillator signals 37) from the local oscillator 38. The output terminal of the mixer circuit 41 is connected to the input terminal of the output matching circuit 43. Output terminal of the output matching circuit 43 is connected to the IF output port 44.
Matching circuits 32, 43 are provided for the purpose of matching the IF output to a fixed frequency F1 in the IF band, and matching circuits 40, 35 are provided for the purpose of matching the RF output to a fixed frequency F2 (&gt;F1) in the RF band.
For more details of the technology, refer to Y. Takimoto et. al. "Research activities on millimeter wave indoor communication systems in Japan, IEEE MTT-S Digest, 06, pp. 673.about.676, 1993.
FIG. 6 shows another conventional frequency converter used in communication systems. This frequency converter, as in the frequency converter shown in FIG. 5, is comprised by an upconverter 29, a downconverter 30 and a common local oscillator 38 shared by the upconverter 29 and the downconverter 30. Upconverter 29 and downconverter 30 are each provided with respective FETs (field-effect-transistor) 47 and 46 as the mixing elements to comprise the mixing circuit (corresponding to 33, 41 in FIG. 5). The upconverter 29 has a resonance type LC circuit 49 as the element to constitute the matching circuit 32 in FIG. 5 and a strip line 51 as the element to constitute the matching circuit 35 in FIG. 5. The downconverter 30 has a strip line 50 as the element to constitute the matching circuit 40 in FIG. 5, and a resonance type LC circuit 48 as the element to constitute the matching circuit 43 in FIG. 5. In FIG. 6, 52.about.55 refer to strip lines.
For further details of the device shown in FIG. 6, refer to M. Madihian et. al. "A monolithic AlGaAs/InGaAs upconverter IC for K-band wireless network", IEEE Transactions on Microwave Theory and Techniques, Vol. 43, No.12, pp2773.about.2778, Dec. 12, 1995, for example.
One of the problems of the devices shown in FIGS. 5 and 6 is that the devices occupy a large space so that the integrated circuit manufacturing cost is increased in proportion to the amount of space required on the IC substrate.
In other words, to obtain a complete transceiver using such a design concept, it is necessary to provide four ports: IF input port 31; IF output port 44; RF input port 39; and RF output port 36. In general, external connection sections for IF and RF input and output pads consume some substrate area, causing an increase in the overall area of the device. Also, the mixing circuits 33, 41 that constitute the respective upconverter 29 and downconverter 30 (or FETs 47, 46 serving as the mixing elements to constitute the mixer circuits 33, 41) also require own matching circuits for the corresponding input/output regions, leading to an overall requirement of four matching circuits.
Another problem in the design of the devices shown in FIGS. 5 and 6 is that it is not possible to appropriately modify a target frequency to achieve matching, within the IC circuitry. The reason is that the matching circuits have respective fixed frequencies so that a target frequency to achieve matching are invariant.